Determining how morphological differences arise is a subject of great importance in evolutionary biology but one that has been very difficult to address experimentally. However, with the recent advent of the field of evolutionary and developmental biology (evo-devo), it is now becoming feasible to bring new and interesting species into the lab to ask molecular and genetic questions. Most evo-devo studies either focus on macroevolution (large-scale) or microevolution (small-scale). Microevolutionary studies have been very valuable in discovering genetic changes causing morphological change because the time difference separating the populations in question is relatively short. One question that still remains is whether the path of microevolutionary change represents on a shorter time scale the path of changes on a larger time scale. To really understand the evolution of morphological change in speciation, we need to address the seemingly impossible goal of looking at the genetics of morphological evolution in species separated by great time differences. One way of bridging the gap between evolution on a short time scale and evolution on a longer time scale is to look at a morphology that shows great diversity both within species and between species. We propose to study antennal development molecularly and genetically across three different time scales: between insects and crustaceans, between different crustacean species, and within a crustacean species that has intraspecific antennal variation. We will be using a candidate gene approach, assaying gene expression of genes known to be involved in antennal development in insects in crustacean species with differing antennal morphologies. We will also functionally pursue some of these genes in the crustacean Parhyale hawaiensis, a species amenable to molecular analyses. Using a candidate genetic approach, we will examine intraspecific antennal variation in a species that has cave and surface dwelling populations. Studying the genetic and molecular basis behind phenotypic change is very important from a medical standpoint; one of the major goals in human genetics is to figure out what genetic changes are responsible for diseases and other conditions. Understanding the genetic and molecular basis of phenotypic change in species in which laboratory experiments are possible will allow insight into the process of evolution: what types of genes are affected, what types of mutations are in these genes, and how much of the variation in a particular trait is encoded genetically and environmentally. This information will yield a greater understanding of evolutionary change which will be helpful in the analysis of the human genome.